In addition to breeding bird populations, various bird species stop regularly in Iceland while travelling between their breeding and wintering areas. Others are winter or summer visitors. Some of these visitors also have breeding populations in Iceland, or can be both passage migrants and winter visitors.
Several bird species spend several weeks here in Iceland in spring and autumn during their migrations between their northern breeding grounds and their wintering grounds in the British Isles and elsewhere in western Europe. The best known of these are three goose species:
Other passage migrants include the long-tailed jaeger (Stercorarius longicaudus), which is known to have bred here, and the pomarine jaeger (Stercorarius pomarinus). These migrants pass through the waters surrounding Iceland and occasionally also fly over Iceland.
Many species that breed in Iceland also travel across the country en route to more northerly breeding grounds, including the pink-footed goose (Anser brachyrhynchus), dunlin (Calidris alpina), and snow bunting (Plectrophenax nivalis).
Several bird species arrive in autumn in Iceland to spend the winter but are rarely seen at other times of year. These winter visitors include the Iceland gull (Larus glaucoides) from Greenland and northeastern Canada, which is a common bird with a wide distribution around the Icelandic coast, and the king eider (Somateria spectabilis), which presumably arrives from Greenland. Winter brings an abundance of certain bird species that also have breeding populations in Iceland, such as eiders from Northeast Greenland and Svalbard and auks from Svalbard and elsewhere.
Two petrel species (Procellariiformes) come to Iceland from their breeding grounds in the southern hemisphere. They arrive in spring and remain in Icelandic waters during the summer and even into the autumn. The sooty shearwater (Ardenna grisea) is today seen mainly in the waters to the south of Iceland in August and into the beginning of October. The great shearwater (Puffinus gravis) is a more rare visitor than it once was, and sightings occur primarily in the ocean to the south and west of Iceland in the first half of summer.
The majority of bird species that have been sighted in Iceland are classified as vagrants. These birds have strayed or been sent off course during seasonal migration between other countries or joined a flock of related species. Some vagrant bird species are fairly common and come to Iceland on an annual basis, such as the blackcap (Sylvia atricapilla), which arrives mainly in the autumn. Others are extremely rare, and many have only been sighted here once. Information on rarities has been collected in an organised manner for decades. An annual summary is published in the periodical Bliki. In this way, it has been possible to gain an overview of this group of birds, including data on colonisation by various birds that have been establishing a regular breeding presence in Iceland in recent years, such as the common shelduck (Tadorna tadorna) and goldcrest (Regulus regulus).